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I'm designing a digital clock for a freshman electrical engineering projects course. I am using SN74HC161 4-bit synchronous counter chips for the counting. My design counts seconds and minutes with correct rollovers, and I am going to design the hour logic next.

I am wondering if it is even possible to load values onto my counters as soon as the clock powers up. My counter begins from zero, but I want the clock to default to midnight, for example, because 0 o'clock does not exist. Though I will be adding a feature to set the clock's time (by manually incrementing hours), I don't want my clock to start off with zeros across all my seven segment displays.

This low-res picture is just for a general idea of my design. I am using NI Multisim (and yes, I understand this is a noob-ish piece of software, but I am a freshman electrical engineering student).

Clock Design

Here is a closeup of my counter / decoder chips so you can makeout the pinout.

enter image description here

Any help would be greatly appreciated.

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  • \$\begingroup\$ Perhaps that's what that pin labeled "load" is all about \$\endgroup\$ – Scott Seidman Apr 9 '16 at 1:54
  • \$\begingroup\$ Obviously. But upon startup this becomes a bit tricky and I would appreciate helpful feedback. \$\endgroup\$ – Matt D Apr 19 '16 at 7:36
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I'm having trouble seeing the pins on your parts, but I believe I see a 'clear' or 'reset' input. If you place an RC circuit that goes into a Schmitt trigger and run the Schmitt trigger into your clear outputs, then at power up, the resets will all be held until the RC charges, typically a few milliseconds.

Looks like fun!

Edited to add a schematic using a comparator instead of a dedicated Schmitt trigger. Same idea. Set the delay using R1 and C1. Set the threshold using R2 and R3. If you need to invert, then keep R4 where it is and reverse the voltage divider and the RC circuit.

schematic

simulate this circuit – Schematic created using CircuitLab

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Those A,B,C,D pins on your 74LS161 is for parallel input applying a 5v to a pin represents a logic 1 and grounding it represents a logic 0, you can set the two ic's pins to 0001(1 in binary) and 0010(2 in binary) then a signal to the load pins will reset to these these inputs. so to do this at start-up you need to put a not gate on all the outputs(for 0000 binary) run it through an and gate and put the output to the load pin

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